Obstacle detection device for vehicle

ABSTRACT

If the maximum time width Lt of the intensity of received light of reflected waves from a vehicle ahead is smaller than a reference time width, it is judged that the vehicle ahead is positioned in proximity to the detection limit distance of an obstacle detection device for vehicle. Thus, there is no problem, for example, even if a cut-in vehicle is present in reality between the vehicle ahead and the vehicle of interest and nevertheless, the distance to the cut-in vehicle cannot be detected. It can be judged whether the vehicle ahead is positioned in proximity to the detection limit distance of the device by judging the magnitude relation between Lt and the reference time width. As a result, the detecting capability of the device can be judged with accuracy.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and incorporates herein by referenceJapanese Patent Application No. 2002-348701 filed on Nov. 29, 2002.

FIELD OF THE INVENTION

The present invention relates to an obstacle detection device forvehicle.

BACKGROUND OF THE INVENTION

Conventionally, there have been various obstacle detection devices forvehicle which detect obstacles around a vehicle. Among them is one thatself-diagnoses the detecting capability of the device itself without anyinspecting device additionally installed (refer to Patent Document 1:JP-A-11-94946 (U.S. Pat. No. 6,147,637), for example). In detectingcapability judgment processing by the obstacle detection device forvehicle disclosed in Patent Document 1, judgment is made as follows: forexample, a vehicle ahead (or preceding vehicle) is driving away from avehicle of interest. The device acquires a distance at which the devicebecomes incapable of detecting the distance to (lose track of) thevehicle ahead (sight end distance). If the average value of the sightend distances acquired by a predetermine number of times is not morethan a predetermined distance, it is judged that the distance detectingcapability has degraded.

When it is thereby judged that the device maintains the normal distancedetecting capability, various types of control are performed. Forexample, following distance control (control wherein the distancebetween the vehicle of interest and the vehicle ahead is kept at apredetermined value) is performed. When it is judged that the devicedoes not maintain the normal distance detecting capability, variousmeasures are taken. For example, control, such as following distancecontrol, is inhibited.

In conventional obstacle detection devices for vehicle, theabove-mentioned detecting capability judgment processing is performed asfollows: a sight end distance is acquired for the judgment of distancedetecting capability where there is no influence of a blind spot. Ifthere is a cut-in vehicle between a vehicle ahead to which the sight enddistance is to be detected and the vehicle of interest, a problemarises. The vehicle ahead is hidden behind the cut-in vehicle and cannotbe detected (creation of blind spot). The distance at which the vehicleahead becomes undetectable can be erroneously judged as a sight enddistance. To cope with this, the following measure is taken: Overlappingof the vehicle ahead and the cut-in vehicle is checked based oncoordinate data indicating the past positional relation between thevehicles in the direction of the width of vehicle. If it is revealedfrom the result of the check that track of the vehicle ahead has beenlost by the cut-in vehicle, detecting capability judgment based on theacquired sight end distance is inhibited.

However, this poses a problem. In the conventional detecting capabilityjudgment processing, judgment is made based on coordinate data whichindicates the positional relation between the vehicle ahead and thecut-in vehicle. In other words, the judgment processing is on theprecondition that both the vehicle ahead and the cut-in vehicle havebeen detected.

There is a case where a cut-in vehicle is actually present between avehicle ahead and the vehicle of interest but reflected waves sufficientfor distance detection cannot be obtained from the cut-in vehiclebecause of, for example, dirt on the rear part of the cut-in vehicle. Inthis case, the distance to the vehicle ahead which has been hiddenbehind the cut-in vehicle and undetectable is judged as the sight enddistance, and the distance detecting capability is judged using thissight end distance.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-mentioned problems. The present invention is intended to providean obstacle detection device for vehicle wherein detecting capabilityjudgment can be made with accuracy even if the distance to anothervehicle present between the vehicle ahead and the vehicle of interest isundetectable.

According to the present invention, an obstacle detection device forvehicle comprises: radar means which radiates transmitted waves around avehicle and detects reflected waves of the transmitted waves; sensingmeans which senses a distance to an obstacle around the vehicle based ona result of detection of the reflected waves by the radar means;determining means which determines a limit distance within which sensingby the sensing means is possible; and judging means which compares thelimit distance determined by the determining means with a preset sensingreference distance and judges an operating state of the device. Theobstacle detection device for vehicle is characterized in that thesensing means comprises signal level judging means which judges a signallevel of the reflected waves. The obstacle detection device is alsocharacterized in that the determining means determines the limitdistance based on the result of detection of the reflected waves whosesignal level is lower than a preset signal level.

As mentioned above, the obstacle detection device for vehicle of thepresent invention determines limit distances from the result ofdetection of reflected waves whose signal level is lower than a presetsignal level. In case of a radar means using light waves, for example,laser light is radiated (emitted) and reflected waves are reflected byan obstacle. The signal level of the reflected waves (the brightness oflight in the form of reflected wave) varies according to the distance tothe obstacle. More specifically, when the distance to the obstacle islong, the signal level is low as a rule. When the distance to theobstacle is short, the signal level is high.

Therefore, if a limit distance which can be sensed by the sensing meansis detected, it is obvious that the signal level of the detectedreflected waves is low. If the signal level is lower than a presetsignal level, the limit distance is determined from the result ofdetection of the reflected waves at that signal level.

Thus, even if any vehicle (a cut-in vehicle) or object is present onthis side of a vehicle ahead in reality and is undetectable because ofdirt on it or the non-reflectiveness of it, there is no problem. As longas the signal level of reflected waves from the vehicle ahead is equalto or above a preset signal level, the distance to the vehicle ahead isprevented from being judged as a sight start distance or sight enddistance. As a result, the detecting capability of the device can bejudged with accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a block diagram illustrating the constitution of the vehiclecontroller 1 in an embodiment of the present invention;

FIG. 2 is a block diagram illustrating the constitution of the scanningdistance measuring equipment of the vehicle controller in the embodimentof the present invention;

FIG. 3 is a flowchart illustrating the main routine in the embodiment ofthe present invention;

FIG. 4 is a flowchart illustrating target sensing processing in theembodiment of the present invention;

FIG. 5 is a flowchart illustrating target data update processing in theembodiment of the present invention;

FIG. 6 is a flowchart illustrating detecting capability judgmentprocessing in the embodiment of the present invention;

FIG. 7 is an explanatory drawing illustrating the way a vehicle ahead Bchanges lanes at time [t-4] in the embodiment of the present invention;

FIG. 8 is an explanatory drawing illustrating the way the vehicle aheadB changes lanes at time [t-3] in the embodiment of the presentinvention;

FIG. 9 is an explanatory drawing illustrating the way the vehicle aheadB changes lanes at time [t-2] in the embodiment of the presentinvention;

FIG. 10 is an explanatory drawing illustrating the way the vehicle aheadB changes lanes at time [t-1] in the embodiment of the presentinvention;

FIG. 11 is an explanatory drawing illustrating the way the vehicle aheadB changes lanes at time [t] in the embodiment of the present invention;

FIG. 12 is an explanatory drawing illustrating the way a vehicle ahead Bcuts in at time [t-3] in the embodiment of the present invention;

FIG. 13 is an explanatory drawing illustrating the way the vehicle aheadB cuts in at time [t-2] in the embodiment of the present invention;

FIG. 14 is an explanatory drawing illustrating the way the vehicle aheadB cuts in at time [t-1] in the embodiment of the present invention;

FIG. 15 is an explanatory drawing illustrating the way the vehicle aheadB cuts in at time [t] in the embodiment of the present invention;

FIG. 16 is an explanatory drawing illustrating fail judgment processingin the embodiment of the present invention; and

FIG. 17 is a waveform chart of reflected waves illustrating theprinciple of distance measurement in the embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the obstacle detection device for vehicle inthe embodiment of the present invention will be described below. In thisembodiment, the obstacle to be detected is a vehicle ahead, anddetecting capability judgment is made on the obstacle detection devicefor vehicle based on detection data from the vehicle ahead.

FIG. 1 illustrates the constitution of a vehicle controller to which theobstacle detection device for vehicle in this embodiment is applied. Asillustrated in the figure, the vehicle controller 1 detects any vehicleahead by the scanning distance measuring equipment 3 as a radar means.The vehicle controller 1 performs either or both of two different typesof control according to the setting of a mode switch (not shown): rearend collision preventive control and tailing cruising control (followingdistance control). Under rear end collision preventive control, anaudible alarm is generated when the vehicle ahead gets in apredetermined alarming range in front of the vehicle of interest. Undertailing cruising control, the vehicle speed is controlled so as to keepthe distance between vehicles at a predetermined value.

As illustrated in the figure, a detection signal from the scanningdistance measuring equipment 3 is inputted to an electronic controlcircuit 5. Based on the inputted detection signal, the electroniccontrol circuit 5 senses the vehicle ahead as described later. Further,the electronic control circuit 5 outputs a driving signal to a distanceindicator 7 to indicate the distance between the vehicle of interest andthe vehicle ahead.

Further, if the vehicle ahead gets in the alarming range with rear endcollision preventive control mode selected, the electronic controlcircuit 5 outputs a driving signal to an audible alarm generator 9 togenerate an audible alarm. The electronic control circuit 5 is connectedwith an alarm sound volume setter 11 and an alarm sensitivity setter 13.Thus, the sound volume of audible alarm and the alarm sensitivity aresettable.

With tailing cruising control mode selected, the electronic controlcircuit 5 outputs an driving signal also to the following items tocontrol vehicle speed: a throttle driver 15 which drives a throttlevalve; a brake driver 17 which drives brakes; and an automatictransmission controller 19 which controls an automatic transmission.

Further, the electronic control circuit 5 is connected with: a vehiclespeed sensor 21 which outputs signals corresponding to the vehiclespeed; a brake switch 23 which outputs signals corresponding to theoperating state of brakes; and a throttle angle sensor 25 which outputssignals corresponding to the opening of the throttle valve. Thus, theelectronic control circuit 5 receives data required for varied control.

Further, the electronic control circuit. 5 is connected with a powerswitch 27 which supplies power from a power circuit (not shown) inconjunction with key switch operation. Furthermore, the electroniccontrol circuit 5 outputs a driving signal to a sensor trouble indicator29 which announces any trouble in the individual sensors 21 to 25.

Next, referring to the block diagram in FIG. 2, the constitution of thescanning distance measuring equipment 3 will be described. Asillustrated in FIG. 2, the scanning distance measuring equipment 3 isconstituted mainly of a transmission-reception unit 31 and an operationunit 33. The transmission-reception unit 31 includes a semiconductorlaser diode (hereinafter, referred to just as “laser diode”) 39 whichradiates pulsed laser light H through a scan mirror 35 and a lightemitting lens 37; and a photoreceptor 43 which receives the laser lightH reflected by an obstacle (not shown) and outputs voltage correspondingto the intensity of the received light.

The laser diode 39 is connected with the operation unit 33 through adrive circuit 45, and radiates (emits) laser light H according to adriving signal from the operation unit 33. The scan mirror 35 isprovided with a polygonal mirror 47 rotatably installed. When a drivingsignal is inputted from the operation unit 33 through a motor drive unit49, the polygonal mirror 47 is rotated by driving force from a motor(not shown). Then, laser light H is sweepingly radiated through apredetermined angle ahead of the vehicle of interest.

The output voltage of the photoreceptor 43 is amplified to apredetermined level through a preamplifier 51, and then inputted to avariable-gain amplifier 53. The variable-gain amplifier 53 is connectedwith the operation unit 33 through a D-A converter 55. The variable-gainamplifier 53 amplifies input voltage in accordance with a gain specifiedby the operation unit 33, and outputs the voltage to a comparator 57.The comparator 57 compares the output voltage V of the variable-gainamplifier 53 with a predetermined voltage V0, and inputs a predeterminedlight reception signal to a time measurement circuit 61 when V>V0.

The time measurement circuit 61 is also fed with the driving signaloutputted from the operation unit 33 to the drive circuit 45. Thedifference in input time between the driving signal and the lightreception signal is measured, and the measured value is inputted to theoperation unit 33. Based on the input time difference from the timemeasurement circuit 61 and the rotation angle of the polygonal mirror 47at that time, the operation unit 33 computes the distance to and thedirection of the obstacle. The output voltage V of the variable-gainamplifier 53 is also inputted to a peak hold circuit 63, and the peakhold circuit 63 inputs the maximum value of the output voltage V to theoperation unit 33.

The thus constituted scanning distance measuring equipment 3 measuresdistances on the following principle: FIG. 17 is a waveform chart ofreflected waves illustrating the principle of distance measurement. Thecurve L1 corresponds to reflected waves whose intensity of receivedlight is relatively high. The curve L2 corresponds to reflected waveswhose intensity of received light is relatively low.

In the figure, it is assumed that a time when the rising curve L1crosses a predetermined voltage V0 set by the comparator 57(hereinafter, referred to as “threshold”) is t11, a time when thefalling curve L1 crosses the threshold V0 is t12, and the timedifference between time t11 and time t12 is Δt1. Further, it is assumedthat a time when the rising curve L2 crosses the threshold V0 is t21, atime when the falling curve L2 crosses the threshold V0 is t22, and thetime difference between time t21 and time t22 is Δt2. The threshold V0is set for the purpose of preventing the influences of noise components.

As is evident from FIG. 17, when the time difference Δt1 correspondingto intense reflected waves and the time difference Δt2 corresponding toweak reflected waves are compared with each other, a relation expressedas Δt1>Δt2 holds. That is, the magnitude of time differences (Δt1 andΔt2) determined by times (t11, t12, t21, and t22) when the waveform ofreceived reflected waves crosses the threshold V0 corresponds to theintensity of received light. When the intensity of received light islow, the time difference is small (Δt2). When the intensity of receivedlight is high, the time difference is large (Δt1). Therefore, the timedifferences make an index which characterizes the intensity of receivedreflected waves. Hereinafter, the time differences will be referred toas time width corresponding to intensity of received light (Δt1, Δt2).

Based on intermediate times in time widths corresponding to intensity ofreceived light (Δt1, Δt2), predetermined correction is performed tocompute a time tp when the maximum voltage is reached. Based on the timedifference between when the laser diode 39 emits light and a time tpwhen the maximum voltage is reached, the distance to the obstacle ismeasured.

The intensity of received light corresponds to the distance to theobstacle as a rule. That is, when the distance to an obstacle is short,reflected waves whose intensity of received light is high are obtained.When the distance to an obstacle is long, reflected waves whoseintensity of received light is low are obtained. Hence, when thedistance to an obstacle is short, the time width corresponding tointensity of received light tends to be increased. When the distance toan obstacle is long, the time width corresponding to intensity ofreceived light tends to be reduced.

When the operation unit 33 has computed the distance to and thedirection of an obstacle as mentioned above, the operation unit 33inputs the result of the computation (hereinafter, referred to as“two-dimensional distance data”) to the electronic control circuit 5.Then, the electronic control circuit 5 performs target sensingprocessing and detecting capability judgment processing to be describedlater. In addition to the two-dimensional distance data, the operationunit 33 also inputs to the electronic control circuit 5 time widthscorresponding to intensity of received light used in distancecomputation.

Next, control processing performed by the electronic control circuit 5will be described. FIG. 3 is a flowchart illustrating the main routineexecuted by the electronic control circuit 5. The electronic controlcircuit 5 executes this processing every 0.1 second. As illustrated inthe figure, after the processing is started, two-dimensional distancedata and time widths corresponding to intensity of received light areread in at Step 70.

At Step 80, target sensing processing is performed to sense individualvehicles or the like to be sensed as a target. At Step 90, detectingcapability judgment processing is performed to judge whether the deviceis capable of detecting the distance to a target (e.g. vehicle ahead)with accuracy. Then, the processing is terminated once.

Subsequently, target sensing processing at Step 80 will be described.This processing is performed every 0.1 second. Major part of the targetsensing processing is the same as target sensing processing inJP-A-H7-318652 (corresponding to U.S. Pat. No. 5,574,463) for which theapplicant applied for a patent, and the description of the processingwill be simplified.

After the processing is started, Step 103 is carried out as illustratedin FIG. 4. At Step 103, based on two-dimensional distance data from theoperation unit 33, the position of the obstacle is recognized asdiscontinuous dots. Of these dots, those that gather adjacently are,unified and recognized as a segment (line segment) having only thelength in the direction of the width of vehicle. “Gathering adjacently”is defined as a condition that the spacing in the X-axis direction, orthe direction of the width of vehicle, is equal to or less than theinterval of laser light H radiation and the spacing in the Y-axisdirection, or the longitudinal vehicle direction, is less than 3.0 m.

Further, of the dots constituting a segment, one whose time widthcorresponding to intensity of received light is largest is selected. Theselected dot is correlated to the segment as a time width representativeof the segment and is temporarily stored.

In the subsequent Step 105, “1” is substituted for a variable i. At Step107, it is judged whether target Bi is present. Target Bi (i is anatural number) is a model of an obstacle created for each of segmentsby the processing described later. Since there is no created target Biat start, negative judgment is made, and the operation proceeds to thesubsequent Step 111.

At Step 111, it is judged whether any segment without correspondingtarget Bi is present. There is no created target Bi at start asmentioned above. Therefore, if segments are recognized at Step 103, allthe segments are those having no corresponding target Bi. In this case,affirmative judgment is made, and the operation proceeds to Step 112.

At Step 112, it is judged whether the number of targets Bi is less thana predetermined value (PV). (The predetermined value is a value obtainedby adding a margin to the upper limit value of the number of obstacleswhich emerge within a predetermined angle through which laser light H issweepingly radiated.) Since the number of targets Bi is less than thepredetermined value at start, affirmative judgment is made, and theoperation proceeds to Step 113.

At Step 113, target Bj (j=1, 2, . . . ) is created for the individualsegments in decreasing order of proximity to the vehicle, and theprocessing is terminated once. If the total number of targets reachesthe predetermined value while target Bj is sequentially created, targetBj is not created any more.

Each target Bj has the following pieces of data: the coordinates of thecenter (X, Y), width W, relative speeds in X-axis direction and inY-axis direction VX and VY, status flag Fj, time width corresponding tointensity of received light Ltj representative of the target, and thelike.

When target Bj is created, these pieces of data are set as follows: forthe coordinates of the center (X, Y) and width W, the coordinates of thecenter and the width of the segment are used without modification. Thisis the same with time width corresponding to intensity of received lightLtj. For VX, VY, Fj, and data pieces representing the past eightmeasurements, the following setting is used: VX=0; VY=(vehiclespeed)^(−1/2) (=(vehicle speed) to the power of negative one half);Fj=0; and data pieces representing the past eight measurements are madeempty. The status flag Fj is a flag which indicates whether target Bj isin pending status, sensed status, or extrapolated status. (Thedefinition of each status will be described later.) In pending status,Fj=0 is set. When target Bj is created, pending status is set.

If it is judged at Step 107′ that the segment relates to target Bi, theoperation proceeds to Step 121, and the segment corresponding to thetarget Bi is detected. The definition of “segment corresponding totarget Bi” is found in the description based on FIG. 8 in U.S. Pat. No.5,574,463. The selecting method for segments is also the same as in thedescription in connection with FIGS. 9, 10 in the same US patent.Therefore, the description of them will be omitted.

At the subsequent Step 123, target Bi update processing to be describedlater is performed according to presence/absence of a correspondingsegment. At Step 125, “1” is added to the variable i, and then theoperation proceeds to Step 107.

Next, target data update processing wherein target Bi is updated will beillustrated in the flowchart in FIG. 5. After the processing is started,it is judged at Step 201 whether a corresponding segment was detected atStep 121. If the segment was detected, it is judged at Step 202 whetherthe count on a presence counter Cai is 4 or more. The presence counterCai is incremented when a segment is present.

If the count on the presence counter Cai is less than 4, the processingis once terminated after the present counter Cai which counts times whenthere is a corresponding segment is present is incremented (not shown).If the count on the presence counter Cai is not less than 4, theoperation proceeds to Step 203, and “1” is set on Fi to indicate thattarget Bi is in sensed status. At Step 205 and Step 207, an absencecounter Cni which counts times when there is no segment corresponding totarget Bi is reset. Further, the presence counter Cai is incremented.

At the subsequent Step 209, using data of the corresponding segment, thedata of target Bi is updated, and then the operation returns to the mainroutine. This target Bi data update processing will be described infurther detail. A corresponding segment as mentioned above has data onthe coordinates of the center and the width. It is assumed that thesepieces of data are (Xs, Ys) and Ws. Then, the new coordinates of thecenter and the new width of target Bi are (Xs, Ys) and Ws like thecorresponding segment. Further, the time width corresponding tointensity of received light Lti, representative of target Bi, is updatedwith the maximum time width among the individual segments. The newrelative speeds (Vx, VY) of target Bi are expressed by the followingexpression:(VX, VY)=((Xs−Xk)/dt, (Ys−Yk)/dt)  [Expression 1]

where, (Xk, Yk) is the oldest one of the past center's coordinate dataof target Bi (Target. Bi has data from up to eight times of measurementin the past); and dt is a time which has passed after the measurement ofthe center's coordinate data.

If there is no segment corresponding to target Bi at Step 201, theoperation proceeds to Step 211. Then, it is judged whether the statusflag Fi of the target Bi is set to “2”, which indicates extrapolatedstatus. If this is the first time to proceed to this processing, Fishould be 0 or 1. Therefore, negative judgment is made, and theoperation proceeds to Step 213.

At this step, it is judged whether the count on presence counter Cai is6 or more. If Cai is less than 6, the operation proceeds to Step 215.Then, all the data related to target Bi is erased, and the operationreturns to the main routine. In other words, as long as a segmentcorresponding to target Bi is detected, the processing of Steps 201 to209 is repeated, and the count on the presence counter Cai is graduallyincreased. If at Step 213, track of target Bi is lost before six cycleshave not passed, the data related to the target Bi, is erased.

By this processing, data of temporarily detected target Bi can beerased. Thus, unnecessary data of objects on the roadside can beremoved, and the obstacle (target Bi) can be sensed with higheraccuracy.

If it is judged at Step 213 that Cai is not less than 6, that is, iftarget Bi is followed for six cycles or longer and then track of it islost, the operation proceeds to Step 221. Then, it is judged that targetBi is in extrapolated status, and the status flag Fi is set to 2. At thesubsequent Step 225, 1 is added to the count on the absence counter Cni.

At the subsequent Step 227, it is judged whether the count on theabsence counter Cni has become 5 or more. If the count on the absencecounter Cni is less than 5, the operation proceeds to Step 229. Then,the data of target Bi is updated with computed values, and the operationreturns to the main routine. That is, it is assumed that the relativespeeds (VX, VY) and the width W do not change, and the coordinates ofthe center (X, Y) of target Bi are computed.

As explained above, if target Bi is followed for six cycles or longerand then track of it is lost, it is judged that the target Bi is inextrapolated status (Fi=2), and the subsequent data of target Bi isupdated with computed values (Step 229). At this time, the operationproceeds from Step 221 directly to Step 225, and t the absence counterCni is gradually incremented. If the count on the absence counter Cnibecomes 5 or above, that is, if track of target Bi is lost for 5successive cycles or longer, the operation proceeds to Step 215, and thedata on target Bi is erased.

Because of the above-mentioned processing, even if track of an obstacle(target Bi) which has been followed for six cycles or longer and thepresence of which has been confirmed is temporarily lost, there is noproblem. If the obstacle is found again (Step 201), track of theobstacle can be followed as the identical obstacle again.

In FIG. 4 back again, when the data of all target Bi (i=1, 2, . . . )has been updated by the processing comprising Steps 107, 121, 123, and125, there is no target Bi corresponding to the incremented variable iremaining at 125. Then, negative judgment is made at Step 107, and theoperation proceeds to Step 111 as mentioned above.

If there is a segment which does not correspond to any target Bi (Step111), new targets Bj in a number within the predetermined value arecreated for each segment in the processing of Step 112 and the followingstep (Step 113). Then, the processing is terminated once. If all thesegments correspond any target Bi (Step 111), the processing is directlyterminated.

By the above-mentioned processing, it can be favorably judged whether anobstacle recognized as a segment is identical with target Bi sensed inthe past. Therefore, the relative speeds (VX, VY) of an obstaclecorresponding to target Bi relative to the vehicle of interest can becomputed with accuracy.

Next, detecting capability judgment processing performed at Step 90,which is characteristic of this embodiment, will be described referringto the flowchart in FIG. 6. This processing is performed every 0.1second. At Step 301 in FIG. 6, it is judged whether the vehicle ofinterest is presently in (a) state in which the vehicle of interest isapproaching the vehicle ahead. If affirmative judgment is made here, theoperation proceeds to Step 303. If negative judgment is made, theoperation proceeds to Step 305.

More specifically, this judgment of (a) is made when the status of thetarget (vehicle ahead) changes from pending status to sensed status forthe first time. That is, the judgment is made when the detection time inpending status becomes at least 0.4 second or above (the target isdetected for four successive cycles at a rate of 0.1 second per cycle,for example). Pending status is unstable status soon after the detectionof a target is started. Sensed status is status in which the target isbeing detected with stability.

At Step 303, when the status changes from pending status to sensedstatus, that is judged as the start of the sight of the vehicle ahead.Therefore, at Step, 303, in (a) state in which the vehicle of interestis approaching the vehicle ahead, it is judged whether executionconditions for performing this processing are met. If affirmativejudgment is made here, it is judged that the execution conditions forperforming this processing are met, and the operation proceeds to Step309. If negative judgment is made, it is judged that the executionconditions are not met, and the processing is terminated once.

The following criteria (1) to (6) are applicable for the executionconditions for this processing. However, with increase in the number ofcriteria, the device's accuracy of judgment of the capability to detectthe distance between the vehicle of interest and the vehicle ahead(hereinafter, referred to as “detecting capability judgment”) isenhanced.

(1) That the vehicle of interest is driving straight. For example, if itis judged based on a signal from a steering angle sensor (not shown)that the turning radius of the vehicle exceeds 3000 m, the vehicle ofinterest is judged to be driving straight. If the vehicle of interest isconsidered to be driving around a curve, detecting capability judgmentis inhibited. This is because in a curve, track of the vehicle ahead isprone to be lost, and there is a high possibility that any otherobstacle is erroneously judged as the vehicle ahead.

(2) That the vehicle speed of the vehicle of interest exceeds 40kilometers per hour. If the vehicle speed of the vehicle of interest islow, a deviation is prone to be produced between the curvature of theroad calculated from data from the steering angle sensor and the actualcurvature of the road. Further, there is a high possibility that thesituation is unsuitable for detection of sight start distance and thelike, like a congested road. Therefore, if the speed is not more than 40kilometers per hour, detecting capability judgment is inhibited.,

(3) That the relative speed (e.g. VY) relative to the vehicle aheadexceeds 5 kilometers per hour. If the relative speed is low, thefollowing distance does not vary so much, and it is difficult to detecta sight start distance or sight end distance. Therefore, if the relativespeed is not more than 5 kilometers per hour, detecting capabilityjudgment is inhibited.

(4) That the distance to the target exceeds 10 m. If the distance to thetarget is not more than 10 m, there is a low possibility that thevehicle ahead is detected, and there is a high possibility of erroneousdetection due to turbidity in the space. Therefore, if the distance tothe target is not more than 10 m, detecting capability judgment isinhibited.

(5) That the vehicle ahead or the vehicle of interest is not changinglanes (there is not the influence of a blind spot). It is assumed thatthere are vehicles ahead A and B within the limit distance, asillustrated in FIG. 7. If the vehicle ahead B changes lanes and get outof the path, the distance to the vehicle ahead A can be erroneouslyjudged as the sight start distance despite the vehicle being within thelimit distance. In this case, detecting capability judgment isinhibited.

Description will be given more specifically. It is assumed that thevehicle ahead A is detected in sensed status for the first time at time[t] illustrated in. FIG. 11. If there is the vehicle ahead B at a closerdistance, the following conditions are checked. If it is revealed as aresult that there is a target meeting the conditions (the vehicle aheadB is applicable in the figure), it is judged that the vehicle ahead Ahas appeared from a blind spot produced by the vehicle ahead B. Then,detecting capability judgment is inhibited.

FIG. 7 to FIG. 11 illustrate the positional relation between thevehicles and the like for the period from time [t-4] to time [t]. Thefollowing pieces of data are respectively held for up to eight cycles ofpast measurement: the distance to the vehicle ahead A (Ya), the distanceto the vehicle ahead B (Yb), the coordinate of the left end of thevehicle ahead B (Xlb), the coordinate of the right end of the vehicleahead B (Xrb), the coordinate of the left end of the vehicle ahead A(Xla), and the coordinate of the right end of the vehicle ahead A (Xra).

That is, overlapping is checked between the oldest coordinates of theleft and right ends among the pieces of data held with respect to thevehicle ahead B and the coordinates of the left and right ends of thevehicle ahead A at time [t]. If any one of the four conditions listedbelow is met, detecting capability judgment is inhibited. A sign of“maxpast” indicates the oldest data.Xla[t]≦Xlb[maxpast]≦Xra[t]  [Expression 2]Xla[t]≦Xrb[maxpast]≦Xra[t]  [Expression 3]Xlb[t]≦Xla[maxpast]≦Xrb[t]  [Expression 4]Xlb[t]≦Xra[maxpast]≦Xrb[t]  [Expression 5]

If any one of the four conditional expression is met, that indicatesthat the vehicle ahead A and the vehicle ahead B overlapped each otherin the same traveling direction in the past. In this case, it is judgedthat the vehicle ahead B has changed lanes and hence the vehicle ahead Ahas been sensed. Then, detecting capability judgment is inhibited.

(6) That the maximum time width (Lt) of the intensity of received lightcorrelated with a target (vehicle ahead) is smaller than a referencetime width. That is, if the following conditional expression does nothold, detecting capability judgment is inhibited.Lt<(Reference time width)  [Expression]

The processing of Step 303 is performed in (a) state in which thevehicle of interest is approaching (gaining on) the vehicle ahead. Thedistance at which the vehicle of interest starts to sense the vehicleahead at this time is equal to the distance at which the vehicle aheadpositioned in proximity to the detection limit of the device is sensedfor the first time. Then, the time width in which the reflected wavesfrom the vehicle ahead positioned in proximity to the limit distance isover the threshold V0 is short as mentioned above. Therefore, it can bejudged whether the vehicle ahead A is positioned in proximity to thelimit distance by the following procedure: the time width in which thereflected waves from a vehicle ahead positioned in proximity to thelimit distance is over the threshold V0 (reference time width) isdetermined beforehand by experiments or the like. Then, the magnituderelation between the reference time width and Lt is judged.

Thus, even if a vehicle ahead B is present in reality between thevehicle ahead A and the vehicle of interest and nevertheless, thedistance to the vehicle ahead B cannot be detected, that is, even if anyconditional expression in the criterion (5) does not hold, there is noproblem. If the maximum time width Lt of the intensity of received lightof reflected waves from the vehicle ahead A is not less than thereference time width, it can be judged that the vehicle ahead A ispositioned on this side short of the detection limit distance of thedevice. As a result, reflected waves from the vehicle ahead A areprevented from being erroneously used as the limit distance.

If negative judgment is made at Step 301, the operation proceeds to Step305. At Step 305, it is judged whether the vehicle of interest ispresently in (b) state in which the vehicle is receding away from thevehicle ahead. If affirmative judgment is made here, the operationproceeds to Step 307. If negative judgment is made, and the processingis terminated once. More specifically, this judgment of (b) is made whenthe status of the target (vehicle ahead) changes from sensed status toextrapolated status for the first time. In addition, the judgment ismade according to whether the relation expressed as follows holds ornot.The detection time of vehicle ahead>a×(Sight end distance/Relative speedin traveling direction)  [Expression 7]

where, the coefficient a is an experimentally determined value (e.g.0.5). Extrapolated status is status soon after the target (in sensedstatus) which has been detected with stability becomes undetectable. Asmentioned above, the above expression is included in the criteria inaddition to the condition that the status changes from sensed status toextrapolated status for the first time. This is to grasp that thevehicle ahead recedes away and, as a result, becomes undetectable (sightend). For example, if the vehicle ahead B traverses the range ofdetection of the radar located between the vehicle ahead A and thevehicle of interest, the above expression does not often hold.

Therefore, if the conditions including the above expression are met,that is judged as the sight end of the vehicle ahead. If the conditionsare not met, detecting capability judgment is inhibited. At Step 307, in(b) state in which the vehicle ahead is receding away, it is judgedwhether execution conditions for performing this processing are met. Ifaffirmative judgment is made here, it is judged that the executionconditions for performing this processing are met, and the operationproceeds to Step 309. If negative judgment is made, it is judged thatexecution conditions are not met, and the processing is terminated once.

In addition to the above-mentioned criteria (1) to (4), the followingcriteria (7) and (8) are added to the execution conditions for thisprocessing.

(7) That there is no cut-in vehicle between the vehicle of interest andthe vehicle ahead (there is no influence of a blind spot). For example,it is assumed that the vehicles ahead A and B are present within thelimit distance and the vehicle ahead B cuts in and gets into the path,as illustrated in FIG. 12. In this case, the distance to the vehicleahead A can be erroneously judged as the sight end distance despite thevehicle being within the limit distance. Thus, detecting capabilityjudgment is inhibited.

Description will be given more specifically. It is assumed that thevehicle ahead A is brought into extrapolated status for the first timeat time [t] illustrated in FIG. 15. If there is the vehicle ahead B at acloser distance, the four conditions listed below are checked. If theseconditions are met, it is judged that the vehicle ahead A has gotteninto the blind spot produced by the vehicle ahead B, and detectingcapability judgment is inhibited.

FIG. 12 to FIG. 15 illustrate the positional relation between thevehicles and the like for the period from time [t-3] to time [t]. Thefollowing pieces of data are respectively held for up to eight cycles ofpast measurement: the distance to the vehicle ahead A (Ya), the distanceto the vehicle ahead B (Yb), the coordinate of the left end of thevehicle ahead B (Xlb), the coordinate of the right end of the vehicleahead B (Xrb), the coordinate of the left end of the vehicle ahead A(Xla), and the coordinate of the right end of vehicle ahead A (Xra).

That is, overlapping is checked between the oldest coordinates of theleft and right ends among the pieces of data held with respect to thevehicle ahead A and the coordinates of the left and right ends of thevehicle ahead B at time [t]. If any one of the four conditionalexpressions listed below is met, detecting capability judgment isinhibited.Xlb[t]≦Xla[maxpast]≦Xrb[t]  [Expression 8]Xlb[t]≦Xra[maxpast]≦Xrb[t]  [Expression 9]Xla[maxpast]≦Xlb[t]≦Xra[maxpast]  [Expression 10]Xla[maxpast]≦Xrb[t]≦Xra[maxpast]  [Expression 11]

If any one of the four conditional expressions is met, that indicatesthat the vehicle ahead B has been detected in proximity to the distanceat which the vehicle ahead A was detected. In this case, it is judgedthat track of the vehicle ahead A has been lost by the vehicle ahead Bcutting in. Then, detecting capability judgment is inhibited.

(8) That the maximum time width (Lt) of the intensity of received lightcorrelated with a target (vehicle ahead) is smaller than a referencetime width. That is, if the following conditional expression does nothold, detecting capability judgment is inhibited.Lt<(Reference time width)  [Expression 12]

The processing of Step 307 is performed in (b) state in which thevehicle ahead is receding away. The distance at which the vehicle ofinterest comes to fail to detect the vehicle ahead is equal to thedistance at which the vehicle ahead positioned in proximity to thedetection limit of the device is detected for the last time. Then, thetime width in which the reflected waves from the vehicle positioned atthe limit distance is over V0 is short as mentioned above. Therefore, itcan be judged whether the vehicle ahead A has been positioned inproximity to the limit distance by the following procedure: the timewidth in which the reflected waves from a vehicle ahead positioned inproximity to the limit distance is over the threshold V0 (reference timewidth) is determined beforehand by experiments or the like. Then, themagnitude relation between the reference time width and Lt is judged.

Thus, even if a vehicle ahead B is present in reality between thevehicle ahead A and the vehicle of interest and nevertheless, thedistance to the vehicle ahead B cannot be detected, that is, even if anyconditional expression in the criterion (7) does not hold, there is noproblem. If the maximum time width Lt of the intensity of received lightof reflected waves from the vehicle ahead A is not less than thereference time width, it can be judged that the vehicle ahead B ispositioned on this side short of the detection limit distance of thedevice. As a result, reflected waves from the vehicle ahead A areprevented from being erroneously used as the limit distance.

If all the execution conditions for the processing are met in the stateof (a) or (b), an instantaneous value of limit distance obtained bydetection is acquired at Step 309. That is, the value is read as thefirst appropriate measured value of following distance.

At Step 311, it is judged whether the thus obtained measured value oflimit distance has been acquired by a predetermined number n (PN) oftimes (for example, n=5). If affirmative judgment is made here, theoperation proceeds to Step 313. If negative judgment is made, theoperation is terminated once in order to determine the next limitdistance in the next cycle of computation in the same manner asmentioned above.

Step 313, averaging is performed to determine a more accurate limitdistance without the influence of an error. More specifically, the limitdistances acquired by the predetermined number of times are totalized,and the resulting total value is divided by the predetermined number oftimes to calculate the average value of limit distance. At Step 315,fail judgment processing is performed to judge whether the device'scapability to detect distances has actually degraded, as describedlater.

At Step 317, backup data is updated. More specifically, processing isperformed to take the limit distance determined this time as theprevious value for the determination of a new limit distance. By thisprocessing, pieces of data are shifted one by one in time series. AtStep 319, data for averaging is initialized. More specifically,processing to reset the area for storing the instantaneous values oflimit distance, a counter for counting the number of instantaneousvalues and like, and other processing are performed. Then, theprocessing is terminated once.

Next, referring to the flowchart in FIG. 16, the fail judgmentprocessing of Step 315 in FIG. 6 will be described. The fail judgmentprocessing is for judging whether the device's detecting capability (forthe distance between the vehicle of interest and the vehicle ahead)based on the average value of limit distance determined by averaging atStep 313. In this processing, the start and the end of sight of avehicle ahead are discriminated from each other, and respective flagsare set for them.

After the processing is started, judgment is made at Step 401 asillustrated in FIG. 16. The judgment is for deciding whether the averagevalue determined by averaging at Step 313 is less than a predeterminedvalue 1 (PV1) (whether the device's detecting capability has degraded).The predetermined value 1 is a distance (e.g. 50 m) obtained by adding apredetermined margin to the sensing reference distance within which thedevice in condition is capable of sensing obstacles. If affirmativejudgment is made here, the operation proceeds to Step 403. If negativejudgment is made, the operation proceeds to Step 407.

At Step 403, a sensor trouble flag is set (turned on) because it hasbeen judged at Step 401 that the detecting capability of the device hasdegraded. The sensor trouble flag is changed according to the individualsituation. That is, a sight end distance fail flag is set for sight endand a sight start distance fail flag is set for sight start. At S405,the driver is informed of that by lighting up (turning on) the sensortrouble indicator 29, and the processing is terminated once.

At Step 407, it is judged whether the average value determined byaveraging at Step 307 exceeds a predetermined value 2 (PV2) (e.g. 50 m).This is processing for judging whether the detecting capability of thedevice has been recovered. In this case, to prevent frequent change tothe judgment result (chattering), the predetermined values 1 and 2 areprovided with hysteresis.

If negative judgment is made here, it is judged that the detectingcapability of the device has not been recovered. Then, the processing isdirectly terminated once without changing the setting of the sensortrouble flag or the state of the indication. If affirmative judgment ismade, the operation proceeds to Step 409. At Step 409, it is judgedwhether the sensor trouble flag is in the state in which the flag waspreviously set because it has been judged at Step 407 that the detectingcapability of the device has been recovered.

If negative judgment is made here, the processing is terminated once. Ifaffirmative judgment is made, the sensor trouble flag is reset (turnedoff) at Step 411. At Step 413, the indication on the sensor troubleindicator 29 is put out (turned off), and the processing is terminatedonce.

In this embodiment, as mentioned above, the limit distance within whichthe distance to a vehicle ahead can be sensed is detected separately incases where the vehicle of interest is gaining on the vehicle ahead andin cases where the vehicle ahead is receding away. Further, it is judgedwhether the intensity of received light at the time of the detection ofthe limit distance is lower than a preset intensity of received light.Thereby, cases where a vehicle positioned between the vehicle ahead andthe vehicle of interest cannot be detected are coped with. Then, thelimit distance and a predetermined sensing reference distance arecompared with each other. If the limit distance is shorter than thesensing reference distance, it is judged that the device's capability todetect the distance to the vehicle ahead has degraded.

For this reason, degradation in the detecting capability of the devicedue to various causes can be detected with ease and reliability. Suchcauses of degradation in the detecting capability of the device includeexternal conditions, such as rainfall, snowfall, and fog, dirt or thelike sticking to the light emitting system or light receiving system ofthe device, and other causes.

That is, according to this embodiment, degradation in the detectingcapability of the device, erroneous detection, and the like can be foundby self-diagnosis with ease and reliability without any inspectingdevice additionally installed. Since judgment of degradation in thedetecting capability of the device is based on some criteria, thejudgment can be made more precisely. The criteria include that thevehicle of interest is driving straight; that the vehicle of interest isdriving at a speed equal to or above the predetermined value; that thedifference in relative speed between the vehicle of interest and theother vehicle is equal to or above the predetermined value; that thereis no cut-in vehicle between the vehicle of interest and the vehicleahead; that the vehicle of interest or the vehicle ahead is not changinglanes; and that the intensity of received light reflected by the vehicleahead is equivalent to the intensity of received light obtained when avehicle ahead positioned in proximity to the detection limit distance ofthe device is detected.

Further, in the above embodiment, obstacles are detected by radiatingpulsed laser light H by the semiconductor laser diode 39. However, anyother constitution wherein radio waves, ultrasonic waves, or the likeare used may be employed. In this case, the same action and effects asin the above embodiment are obtained. That is, appropriate transmittedwaves can be selected according to the intended use of the scanningdistance measuring equipment 3.

Furthermore, a reference time width can be set as follows. For instance,when the device has in condition a detection limit distance of 150 mahead, a reference time width is set as corresponding to an obstaclebeing 120 m ahead. Thus, even if a vehicle ahead B cuts in between thevehicle ahead A and the vehicle of interest within a 120 m distance fromthe vehicle of interest, there is no problem. If the maximum time widthLt of the intensity of received light of reflected waves from thevehicle ahead A is not less than the reference time width, it can bejudged that the vehicle ahead A is positioned on this side short of thedetection limit distance of the device, namely at most 120 m ahead. As aresult, reflected waves from the vehicle ahead A are prevented frombeing erroneously used as the limit distance.

(Modification)

In the above embodiment, time differences determined by two times atwhich curves corresponding to the intensity of received light cross athreshold V0 are employed as an index which characterizes the intensityof received light. However, the applicable index is not limited to this.As mentioned above, the intensity of received light is converted into avoltage value corresponding to the intensity. Therefore, for example,the maximum voltage value of reflected waves may be employed as an indexwhich characterizes the intensity of received light. The reflected waveswhose intensity of received light is high is shorter in time from whenthe waves are received to when the threshold V0 is reached as comparedwith the reflected waves whose intensity of received light is low.Therefore, the time from when the waves are received to when thethreshold V0 is reached may be employed as an index which characterizesthe intensity of received light. Further, a threshold voltage V1 higherthan the threshold V0 may be provided, and time differences determinedby two times at which curves corresponding to the intensity of receivedlight cross V1 may be employed as an index which characterizes theintensity of received light.

It will be obvious to those skilled in the art that various changes maybe made in the above-described embodiments of the present invention.However, the scope of the present invention should be determined by thefollowing claims.

1. An obstacle detection device for a vehicle comprising: radar meanswhich radiates transmitted waves outside the vehicle and detectsreflected waves of the transmitted waves; sensing means which senses adistance to an obstacle around the vehicle based on a result ofdetection of the reflected waves by the radar means; determining meanswhich determines a limit distance within which the sensing means iscapable of sensing, wherein the determining means determines the limitdistance based on a result of detection of reflected waves whose signallevel is lower than a preset signal level; and judging means whichcompares the limit distance determined by the determining means with apreset sensing reference distance and thereby judges an operating stateof the device, wherein the sensing means includes signal level judgingmeans which judges a signal level of the reflected waves.
 2. Theobstacle detection device according to claim 1, wherein the radar meansradiates light waves and detects reflected waves of the radiated lightwaves, wherein the signal level judging means judges a time width inwhich a voltage value corresponding to an intensity of light in thereflected waves is over a predetermined value, and wherein thedetermining means determines the limit distance based on a result ofdetection of reflected waves whose time width is smaller than a presetreference time width.
 3. The obstacle detection device according toclaim 2, wherein the determining means presets as the reference timewidth a time width in which a voltage value corresponding to anintensity of light in given reflected waves sensed by the sensing meansis over the predetermined value, wherein the given reflected waves arereflected by an obstacle positioned in proximity to the limit distance.4. The obstacle detection device according to claim 2, wherein thesensing means recognizes a position of an obstacle as a segment formedof unified dots that gather adjacently, wherein the segment of unifieddots are a subset of discontinuous dots that are obtained based on aresult of detection of reflected waves, and wherein the determiningmeans determines the limit distance based on a result of detection ofreflected waves of a given dot included in the segment, wherein thegiven dot has a time width in which the predetermined value is exceededis largest among the dots included in the segment.
 5. The obstacledetection device according to claim 1, wherein when the limit distancebecomes less than the preset sensing reference distance, the judgingmeans judges that the device's capability to detect distances hasdegraded.
 6. The obstacle detection device according to claim 1,wherein, when the sensing means continuously senses a given obstacle fora predetermined time or longer after the sensing means senses the givenobstacle for a first time, the determining means determines the limitdistance based on a distance at which the sensing means senses the givenobstacle for the first time.
 7. The obstacle detection device accordingto claim 1, wherein, when the sensing means continuously senses acertain obstacle for a predetermined time or longer and then becomesincapable of sensing the certain obstacle, the determining meansdetermines the limit distance based on a distance at which the sensingmeans becomes incapable of sensing the certain obstacle.